1. Technical Field
The present invention relates generally to the integration of wireless computer network technology in position determination and, more particularly to the use of wireless computer network access points as an additional source of location information to supplement or replace that provided by more conventional sources such as GPS, particularly in environments where traditional methods such as GPS exhibit reduced performance.
2. Description of the Related Art
A number of different techniques are used for position determination of a mobile device. One known technology utilizes satellites in a global positioning system (GPS) constellation. A GPS receiver detects signals from a plurality of GPS satellites and calculates the position of the GPS receiver. If a sufficient number of satellites are detected and the signal quality is good, the GPS receiver can make a highly accurate position determination.
Under certain conditions, the received GPS signals may be insufficient for an accurate position determination. In an alternative, sometimes referred to as mobile-assisted position determination, the data detected by the GPS receiver is transmitted, via a communication network, to a positioning server or position determining entity (PDE). The PDE uses the data provided by the mobile GPS receiver in combination with other location-related data to determine the position of the GPS receiver at the time data was initially received by the GPS receiver. The PDE can determine the position of the GPS receiver with a high degree of accuracy under optimal GPS signal conditions.
Under adverse operating conditions, or in the presence of obstructions, the GPS receiver may be unable to detect the signals from a sufficient number of satellites or those signals may be affected by sources of error such as signal multi-path or dilution of precision, making an accurate position determination difficult. Natural obstructions, such as trees and mountains, may block or deflect signals from the GPS satellites. Man made obstructions, such as buildings and bridges, may also impact signals from the GPS satellites. Under such circumstances, GPS receiver-based positioning may be subject to significant error. This problem is even more pronounced if the GPS receiver is taken indoors. The building walls, metal structures, and the like can severely attenuate the signals from the GPS satellites thus making an accurate position determination very difficult.
Wireless service providers have developed an alternative technique for position determination that does not rely on GPS signals. In a wireless communication system, sometimes referred to as a cellular or cell phone system, a mobile unit receives signals from one or more base transceiver stations (BTS). A typical BTS has an area of coverage, sometimes called a cell, that roughly resembles a circle with the BTS located approximately at the center of the circle or, alternatively, some sector of that circle. Using known techniques, it is possible for a PDE to determine that a mobile unit is located within the area of coverage of a particular BTS and, in some instances, within range of one or more BTS. If the BTS area of coverage is large, the position determination is less accurate. Conversely, if the are of coverage is small, the position determination is more accurate.
A typical BTS uses a multiple antenna array to subdivide a cell into sectors. For example, a particular cell may have three sectors of roughly equal size. Using the techniques described above, it is possible to locate the position of the mobile unit not only within a particular cell, but within a particular sector of that cell. In addition, it is possible to make a rough determination of the distance between the mobile unit and the BTS based on factors, such as signal strength or time delay of a received signal.
For example in one implementation, such as a code division multiple access (CDMA) wireless system, a pilot channel is transmitted by each BTS. The pilot channel allows a wireless cellular telephone to acquire proper timing and frequency reference; the pilot signals can also be used to calculate a phase offset which, when combined with delay information or with offset information from multiple BTSs, can be used to calculate position. Signal strength comparisons between multiple BTSs are also used to determine when to hand off the mobile unit to another BTS. Multiple pilot signals can also be used to trilaterate the position of a mobile unit, or a single pilot used to determine position within a particular cell and/or within a particular sector within that cell. In some technologies, a received signal strength index (RSSI) may also be calculated using known techniques and used to determine an approximate distance between the mobile unit and the BTS. However, the accuracy of such a determination is limited by the inherent inaccuracies in the measurement system described above.
The GPS location system is highly accurate, but does not provide reliable position determination in areas where clear reception of satellite signals are unavailable, such as indoors. A wireless communication system, such as the CDMA system described above, may provide better reliability in detection of signals, but is often less accurate than a GPS system.
Thus, there is a need in the art for an improved position detection system that allows improved position determination while indoors that is less impacted by signal deflection, multi-path and attenuation and further capable of providing location-based services to the consumer. The present invention provides this and other advantages as will be apparent from the following detailed description and accompanying figures.